One of the biggest problems caused by vehicles using fossil fuel, such as gasoline and diesel oil, is the creation of air pollution. A technology of using a secondary battery, which can be charged and discharged, as a power source for vehicles has attracted considerable attention as one method of solving the above-mentioned problem. As a result, electric vehicles (EV), which are operated using only a battery, and hybrid electric vehicles (HEV), which jointly use a battery and a conventional engine, have been developed. Some electric vehicles and hybrid electric vehicles are now being commercially used. A nickel-metal hydride (Ni-MH) secondary battery has been mainly used as the power source for electric vehicles (EV) and hybrid electric vehicles (HEV). In recent years, however, a lithium ion battery has also been used.
High output and large capacity are needed for such a secondary battery to be used as the power source for the electric vehicles (EV) and the hybrid electric vehicles (HEV). To this end, a plurality of small-sized secondary batteries (unit cells) is connected in series to each other so as to form a battery module and a battery pack. According to circumstances, a plurality of small-sized secondary batteries (unit cells) is connected in series and in parallel to each other so as to form a battery module and a battery pack.
In general, such a battery pack has a structure to protect battery modules, each of which has secondary batteries mounted therein. The structure of the battery pack may be varied based on the kind of vehicles or installation position of the battery pack in the vehicles. One of the structures to effectively fix large-capacity battery modules is based on supporting bars and end plates. This structure is advantageous in that movement of the battery modules is minimized even when load is applied toward the supporting bars. To this end, however, it is necessary to sufficiently secure rigidity of the supporting bars and end plates.
In connection with this case, a conventional battery pack including a single battery module is exemplarily shown in a perspective view of FIG. 1.
Referring to FIG. 1, a battery pack 100 includes unit modules 10, each of which has battery cells mounted therein, a base plate 20, a pair of end plates 30, and supporting bars 40.
The unit modules 10 are stacked at the top of the base plate 20 in a state in which the unit modules 10 are vertically erected. The end plates 30 are disposed in tight contact with the outsides of the outermost unit modules 10 in a state in which the lower end of each of the end plates 30 is fixed to the base plate 20.
The supporting bars 40 are connected between the upper parts of the end plates 30 so as to interconnect and support the end plates 30.
However, the battery pack with the above-stated construction does not include a structure to support the battery pack in the forward and backward direction when external force is applied to the battery pack in the forward and backward direction. Furthermore, the battery pack does not include a structure to stably fix the battery cells constituting each unit module. As a result, it is not possible to prevent deformation of the internal structure of the battery pack.
Therefore, there is a high necessity for a battery pack having a specific structure that is capable of minimizing deformation of the battery pack when external force is applied to the battery pack in the forward and backward direction.